Merc V6 History

[1FASTLASER]

I've said once but I'll say it again. This is the most epic thread I have ever had the pleasure of reading. Glad to see you back rckid

[Hoss Marine Propellers]

I've said once but I'll say it again. This is the most epic thread I have ever had the pleasure of reading. Glad to see you back rckid

Yeah ...... What he said!!!! Thanks Again.

[Onetime]

Glad to have you back posting this great history!! Looking forward to more!

[rckid74]

Let’s talk now a little about the piston and cylinder head design. I had made up my mind back at the beginning that I would much prefer a flat top piston as opposed to a crowned one or some other shape. Two main reasons - first, the flat top has the smallest surface area to absorb heat and should run the coolest, very important in any 2-stroke engine. Secondly, compression ratios could readily be changed just by flat milling the head mounting surface. Other advantages were shorter overall height to the top of the plug, ease of machining the piston top, and tighter control of the squish gap. In doing the flow tests on my “Jante Fixture”, I had found that it was easier to get good flow patterns with a domed top piston but with somewhat more effort I could get just as good patterns with a flat top. The only disadvantage I can think of would be that there would be a little greater heat concentration at the timing edge in the area of the exhaust port. We never experimented with domed pistons.
The prototype pistons were made of 356-T6 sand cast aluminum alloy which has about 7-10% silicon content. These worked well. I don’t remember having any problems with them but when we went to the forged production pistons, which had about the same silicon content, we had terrible problems with wrist pin pound-out. Actually, it was a combination of wear and stretching of the hole in the piston. I don’t remember the alloy number of the forged pistons but it was the same as we had been using for years in the in-line 6. At that time I didn’t know of any better alloy to use. We struggled to get the life up on those pistons and we did improve it but it wasn’t until we discovered high silicon (19-23%) hyper-eutectic cast pistons later on that the wrist pin problem went away. These were made by Art Metals, a company in Japan. I believe it was Ray Reid who first tried them in the V6.
I had also decided early on that I wanted to use a hemi head combustion chamber. This stemmed in part at least from my experience driving my fathers 1952 Chrysler New Yorker with it’s hemi-head V8. It was a real torquer. I figured that if they went to all that trouble to put those valves in at odd-ball angles it must have some real advantage over the other chambers. Obvious advantages are short flame travel distance from the plug to the end gasses, and low surface area to volume ratio. The dome was centered and positioned in the head so as to give 55% squish area which was considered optimum. I don’t remember the compression ratio we settled on for the first production.

[Capt.Insane-o]

I never understood why they went away from the (your) nice smooth hemi style chamber to the sharp edged top hat style.Maybe it came with the lost foam and machining costs.

[Dave S]

Better spark plug intrusion. While I was working at a HP shop in NY .....Chip Watkins and Joey Impressas were trying to re-use small chamber heads that had been cut too tight. I said why not Donut chamber.....Put the plug rite in the center of the gas charge. I think Chip found a shop that could cut the heads donut style chamber. The newer 90hp motors have that chamber.... It is good to see an Idea come to use. I only worked there.....as meck. Top hat spark closer to charge. Hemi spark too close the cool metal.

[rckid74]

Another important aspect of the engine was the water cooling system. I had heard of a previous attempt some years before at a V type engine at Mercury which had failed because of cooling problems. It was logical to study OMC’s cooling system and then only make those changes which made sense or were required due to our new configuration. After all, they had been making V engines successfully for many years.
The system is what I would call a double pass in that the water makes two loops thru the block, heads, and covers, entering the bottom of the engine, flowing to the top, back to the bottom, then back to the top, and finally to the bottom and out. This tends to equalize cylinder temps. Initially the cold water from the pump flows thru a passage cast from bottom to top between the banks and along the lower side of the exhaust ports which helps cool the bottom of the exhaust ports. The other side of this passage contacts the crankcase area and this coldest water helps keep the inlet cool for a more dense charge. Then at the top of the block the water crosses over into the exhaust cover where it is preheated some more before passing thru six sets of holes positioned such that it is directed down onto the top of the exhaust ports, the hottest area in the cylinders. Deflectors between the cylinders then cause the water to circulate around the cylinders and up to the top again where it crosses over into the heads and then down and out thru the poppet valve at the bottom of the block.
A thermostat at the top of each head controls water temp at idle. In an attempt at a little cost savings I had made the stupid mistake of putting a single thermostat down at the bottom of the block along side the poppet valve and using the same cover. That was neat and cheap but it didn’t work very well. Joe Harrelson quickly solved the problem and put in the two thermostats, one at the top of each head. However, before he found that solution, the block die had already been made with the opening for the single thermostat next to the poppet valve so that was just not used but it stayed in the block die for years after and I’m sure many people wondered what the heck that was for. I assume it has been deleted by now.
The output flow from the thermostats is carried to the bottom of the block thru hoses and looks like an after thought, which it was. I’ve always hated the look of those hoses hanging out there like that. Had I made the correct decision during the original design, I’d have cast drain passages in the head covers. Ah, hind sight.

[194268]

A few months after I was hired by Doc. Morgan, I think it was Nov. or Dec of '73 I saw prints of the V-6. How close would they have been to production ???

[Dave Strong]

Another important aspect of the engine was the water cooling system. I had heard of a previous attempt some years before at a V type engine at Mercury which had failed because of cooling problems. It was logical to study OMC’s cooling system and then only make those changes which made sense or were required due to our new configuration. After all, they had been making V engines successfully for many years.
The system is what I would call a double pass in that the water makes two loops thru the block, heads, and covers, entering the bottom of the engine, flowing to the top, back to the bottom, then back to the top, and finally to the bottom and out. This tends to equalize cylinder temps. Initially the cold water from the pump flows thru a passage cast from bottom to top between the banks and along the lower side of the exhaust ports which helps cool the bottom of the exhaust ports. The other side of this passage contacts the crankcase area and this coldest water helps keep the inlet cool for a more dense charge. Then at the top of the block the water crosses over into the exhaust cover where it is preheated some more before passing thru six sets of holes positioned such that it is directed down onto the top of the exhaust ports, the hottest area in the cylinders. Deflectors between the cylinders then cause the water to circulate around the cylinders and up to the top again where it crosses over into the heads and then down and out thru the poppet valve at the bottom of the block.
A thermostat at the top of each head controls water temp at idle. In an attempt at a little cost savings I had made the stupid mistake of putting a single thermostat down at the bottom of the block along side the poppet valve and using the same cover. That was neat and cheap but it didn’t work very well. Joe Harrelson quickly solved the problem and put in the two thermostats, one at the top of each head. However, before he found that solution, the block die had already been made with the opening for the single thermostat next to the poppet valve so that was just not used but it stayed in the block die for years after and I’m sure many people wondered what the heck that was for. I assume it has been deleted by now.
The output flow from the thermostats is carried to the bottom of the block thru hoses and looks like an after thought, which it was. I’ve always hated the look of those hoses hanging out there like that. Had I made the correct decision during the original design, I’d have cast drain passages in the head covers. Ah, hind sight.

This great information!! Keep it coming.

Dave

[rckid74]

The “Black Max” intake system ended up being very similar to the then OMC V4 with the six reed blocks set in vertically and three dual throat carbs. However, we did consider using horizontal, straight in reed blocks using dual throat carbs and a special manifold which would deflect the flow from one throat up to the higher cyl. and the other down to the adjacent lower one. See the patent # CA 1144078 A1 by Kieth Gagnier and David Kusche. This manifold presented problems with fuel puddling at low speeds and did increase the fore/aft length of the overall package by an inch or so. For these reasons we decided to stay with the proven design ala OMC.
I don’t now recall what design OMC used for the carb float bowl but I wanted to use a separate float for each cylinder, I.E. six floats. With each nozzle centered in a float the engine would receive a consistent fuel/air ratio even in hard turns. And that is what we used for all the prototype engines and they worked fine. However, before we went into production, I was told by upper management to save some money by going to a single float for each carb, which I did - against my will. Sure enough, after production started we started getting reports of engines running poorly in hard turns so we had to change back to the dual float carbs.
The inlet air box was designed by Dick Lanpheer and it did a very effective job of quieting the induction noise. I can verify that because I was doing some work with the engine on a boat one day and for some reason left the air box cover off and the cowl off. When I started up the engine, I swear, it sounded just like a stacker inline six. It was really loud. There’s a lot of noise coming out of those inlets. It was fun driving it around like that. That boat felt like a tunnel hull.

[Onetime]

Great stuff!

[Scream And Fly]

What an incredible thread. Thank you to everybody that is making this thread incredible!

Greg

[rckid74]

I knew the exhaust system on this narrow angle 60° V6 would be a challenge. There’s not much room between the banks to fit in two separate ducts of adequate area - one for each 3 cylinder bank. It was immediately apparent that I’d have to cast the exhaust chest open as one cavity and then use an inserted divider plate to define the two ducts because the large milling cutter required to cut open the exhaust blisters on the liners had to come in at an angle which would have cut thru any cast-in dividing wall. This also allowed me to gain a little additional area for the exhaust since the divider plate could be cast thinner than a cast-in water cooled wall. Getting a good seal between this divider plate and the block cavity was achieved by using a tongue and groove shape plus a compressed strip of high temp silicone “O”-ring material in the bottom groove. The ends of the dividing wall are only partially sealed by the tongue. Sealing these ends with silicone sealer will show a slight power gain but this was impractical for production.
Cocking the liners at a 30° angle in order to nestle the transfer passages presented a problem with the exhaust snouts. If a single liner was used for both banks, the snouts for one bank would be pointing down - more or less - and the other bank would be pointing up. This would just not do. So I had to bite the bullet and opt for two different liners, one for the starboard side and one for the port. This also meant we’d need starboard and port pistons - undesirable because of the possibility of mix-ups and the obvious cost increase - but necessary.
In the end we had a nice tight exhaust system with very short distances between tuning ports which helped to peak out the torque curve.

[Merc Fanatic]

This is one of if not the best thread I've read on S&F... thank you and please keep it going!!!

[Murph]

, the Best.